In retrospect, it seems obvious that the “secret” show would begin with a prank.

Before the start of a small-scale concert Friday night by Arcade Fire, fans in masks and formal attire thronged in front of a stage decorated with a spinning light and some potted trees. It looked like as if a low-budget prom had been set up in the warehouse-style space, which now serves as an art gallery in the Bushwick neighborhood of Brooklyn. Beamed in light against the back wall: “The Reflektors,” the band’s alias and the name printed on the tickets scored by a few thousand fans.

At about 9:30, James Murphy, the former LCD Soundsystem leader (and a producer of the forthcoming Arcade Fire album), appeared to introduce the Reflektors. A few players took the stage wearing giant paper mache heads. Looking like “Beavis and Butthead” characters come to life, they chugged through some reggae riffs and then shortly shambled off stage–at which point a curtain opened on the far left side of the cavernous room, revealing the real band and causing fans to dash toward the more elaborate stage.

The band broke into the title track of the new album, “Reflektor.” (Alas, without David Bowie, who is on the recorded track. Or perhaps he was lurking somewhere in costume?) Many members wore white suits, including singer Win Butler who also sported a painted-on blue Zorro mask and was flanked by his wife, Regine Chassagne, dressed in an outfit coverd in pink fringes that glowed in the light.

The presence of Murphy was telling. Most of the new songs thrusted with a four-to-the-floor dance beat reminiscent of LCD Soundsystem–or Michael Jackson’s “Billie Jean,” in the case of the song “We Exist.” Other new songs included “Joan of Arc,” which had a more of a punk rock attack, and the triumphant “Afterlife,” which had a Clash-like pulse to it and Butler’s shouted lyric, “If there’s no music in heaven, what’s it for?”

Ticketholders had been warned that costumes or formal wear was mandatory. There were some elaborate get-ups in the crowd–shout out to the woman who kept her pink Pussy Riot balaclava on throughout the sweaty show–but many fans simply went with office attire accessorized with a mask. Between songs, Butler thanked the audience for making an effort: “We figured, we get dressed up every night, so why not you guys.”

He also half-apologized to everyone for the stage switch, especially folks formerly in the front row who had suddenly found themselves at the back when the band appeared. “Do you forgive us? It won’t be the last time we think something’s funny that no one else thinks is funny.”

Keeping up the Reflektors ruse, he said “This is by a Montreal band called Arcade Fire” when leading the band into “Sprawl II.” Another fan-favorite, “Neighborhood #3 (Power Out),” from the band’s debut album, gave way to the new song “Here Comes the Night Time.”

And that was it. After a nine-song set, the band left the stage. Fans hoping that the sub rosa concert venue and Halloween vibe would lead to a marathon performance–or at least an encore–were disappointed when Butler returned to the microphone alone. He explained that the show was over and that instead of awkwardly staring at an empty stage, everyone should hang out, enjoy themselves and dance. When that was met with a scattered boos, he deftly quieted them by explaining that the band members would be coming out to DJ and join in the dancing.

That promise was enough to get some of the audience to linger or head to the makeshift bar for another drink. Other fans called it a night and headed for the exit.